Download CHARACTERIZATION TESTS for the OXYGEN

Experiment # 8: CHARACTERIZATION TESTS for the OXYGEN-CONTAINING COMPOUNDS
SAJOL, Christine Joy.
March 2013
Department of Chemical Engineering, Faculty of Engineering
University of Santo Tomas
España, Manila
Abstract
Tests such as the dichromate test, DNPH (Dinitrophenylhydrazine) test, Tollen’s test, iodoform test, Fehling’s
test and Lucas test would be very useful in determining the type of compound the test solution belongs to. Nine
oxygen-bearing organic compounds, the test solutions, were given namely 1° butyl, 2° butyl, 3° butyl, phenol,
acetone, formaldehyde, benzoic acid, acetamide and ethylacetate In the experiment, the test solution undergone
series of testing to classify the samples from being a primary alcohol, a secondary alcohol, a tertiary alcohol or what
functional group that are presented on the mixture. Another goal of this experiment is to know what types of tests are
particularly used for a specific oxygen-containing compound.
I.
Introduction
The characterization test of oxygen bearing organic compounds is an experiment in which a
variety of tests are available to identify a compound’s property whether it is a primary,
secondary or tertiary alcohol or what functional group does it belong to. The tests that are
included to come up with such results are interconnected with one another like that of the
Dichromate test which is a positive if the mixture turns green-blue, next is DNPH
(dinitrophenylhydrazine) test that has a positive of yellow precipitate, followed by the Tollen’s
test, a positive if there is a silver mirror coating. Next is iodoform test which has a positive of
formation of yellow precipitate. Including the Fehling’s test that has a positive if there’s a red
precipitate and finally the Lucas test to test if the mixture became turbid or not.
Different test solutions are used in this experiment and have different functional groups. Let
us first differentiate and classify the functional groups that are present in this experiment.
Alcohols are compounds in which one or more hydrogen atoms in an alkane have been
replaced by an –OH group. Note however that there are different types of alcohols that are used
in this experiment, the primary, secondary, tertiary and phenol (the –OH group is attached into
an aromatic ring). Alcohols (ROH) can be thought of as derivatives of water in which one of the
hydrogen atoms has been replaced by an alkyl group. If both of the hydrogen atoms are
replaced by alkyl groups, we get ether (ROR). These compounds are named by adding the
word ether to the names of the alkyl groups. Aldehydes (RCHO) and ketones (RCOR') are very
important functional groups, characterized by the presence of an acyl group (RCO-) bonded
either to H (aldehydes) or another C (ketones). Amines (RNH2) are organic derivatives of
ammonia, NH3 and have certain similarities with ammonia. Nitrogen containing compounds are
biologically very important amines, amino acids, amides, proteins, vitamins etc. Lastly,
Carboxylic acids (RCO2H) are the most acidic among of the common organic functional groups.
In this experiment, we’ll be able to characterize on what functional group does the test
solutions belong to and know what particular characterization test must be used in order to
determine a certain functional group of choice.
II.
Review of Related Literature
How does one determine the actual identity and structure of an unknown compound?
This is not a trivial task. Modern x-ray and spectroscopic techniques have made the job
much easier, but for some very complex molecules, identification and structure
determination remain a challenge. In addition to spectroscopic information and information
obtained from other instrumental methods, chemical reactions can provide useful structural
information, and physical properties can contribute significantly to confirming the identity of a
compound. Classification tests, which are simple chemical reactions that produce color
changes or form precipitates, can be used to differentiate alcohols, aldehydes, and ketones
and also to provide further structural information. (Samal, 2009)
The same experiment of characterization test of Tollen’s reagent was conducted by
Rehan Qadri. He noted that when adding the aldehyde or ketone to Tollens' reagent, the
test tube is put in a warm water bath. If the reactant under test is an aldehyde, Tollens' test
results in a silver mirror. If the reactant is a ketone, it will not react because a ketone cannot
be oxidized easily. A ketone has no available hydrogen atom on the carbonyl carbon that
can be oxidized - unlike an aldehyde, which has this hydrogen atom.
Dona Trainor, Adrian Huang and Jim Moyer have stated these things on their website:24 DNP test is for the classifications of aldehydes and ketones and that the positive test for
this classification test is the formation of precipitate. Tollen’s test is also for aldehyde and
the positive test for this is the formation of silver mirror. While the positive test of iodoform
test for methyl ketones is the formation of solid iodoform (yellow). Still on their study, Lucas
test for alcohols have the positive test of appearance of cloudy second layer or emulsion.
The time factor of formation of emulsion for tertiary alcohols is immediate to 2-3 minutes, 510 minutes for secondary and no reaction for primary alcohols. Lastly, the dichromate test,
also known as Jones oxidation, has a positive test for aldehydes and primary or secondary
alcohols consist in the production of an opaque suspension with a green to blue color.
Aldehydes are reducing reagents; they may be oxidized to carboxylic acids (in acidic
solutions) or their salts (in alkaline solution). Positive tests for aldehydes depend on these
facts. For acidified potassium dichromate, if the color changes from orange to green, the
dichromate (VI) has been reduced to chromium (III) and an aldehyde is confirmed. In tollen’s
reagent, if a silver mirror is confirmed in the test tube, this confirms the presence of an
aldehyde. Lastly, for Fehling’s (or Benedict’s) solution, both Fehling’s and Benedict’s
solutions contain complexed copper (II) ions in an alkaline solution. If a red precipitate of
copper oxide is formed, this confirms the presence of an aldehyde.
Same experiment of characterization test was also conducted by Achas M.L., Alvarez
M.A., Bangot K.A., and Bayani K. The experiment dealt with differentiating the various types
of oxygen-bearing organic compounds through several tests, namely Dichromate Test,
Tollen’s Test, DNPH Test, Iodoform Test, and Lucas Test. It was through the use of different
reagents and techniques that the characteristics of each standard compounds were
observed and distinguished. After the reactions have been noted, it was compared to the
reactions with that of the unknown.
III.
Methodology
a. Materials and Equipments
Test Tubes
Beaker
Hot plate
Droppers
6M H2SO4
10% K2Cr2O7
2, 4 DNPH
Tollen’s Reagent
10% KI
5% NaClO
Fehling’s A
Fehling’s B
Concentrated HCL
Anhydrous ZnCl2
95% Ethanol
1° Butyl
2° Butyl
3° Butyl
Phenol
Acetone
Formaldehyde
Benzoic Acid
Acetamide
Ethylacetate
b. Procedure
For the dichromate test, 3 drops of the test solution was putted on a test tube. Then 2 drops
of 10% K2Cr2O7 and 5 drops of 6M H2SO4 were added. The color change and other observable
change were then recorded.
In using the DNPH (dinitrophenylhydrazine) test, 2 drops of the test solution was dropped on
a test tube, 1mL of 95% ethanol was then added and it was followed by the addition of 20 drops
of DNPH. The solutions that don’t have precipitate after 15 minutes was heated for 15 minutes
more.
5 drops of the test solution was added to 2mL of Tollen’s reagent and the observation after 5
minutes was recorded. The solutions that have no visible change were warmed in a hot bath for
5 minutes. This procedure is for the Tollen’s reagent test.
In Iodoform test, 5 drops of the test solution was putted on a test tube and added with 20
drops of 10% potassium iodide. 20 drops of 5% NaClO was carefully added to the test tube and
was warmed in a water bath. The changes in appearance and odor was observed and recorded.
For the Fehling’s test, the 5 drops of the test solution was added with 10 drops of Fehling’s
A and another 5 drops of Fehling’s B. The mixture was warmed until changes are observed. The
changes were then recorded.
In Lucas test, 5 drops of the test solution, 15 drops of concentrated HCL and a pinch of
anhydrous ZnCl2 was combined in a single test tube. The mixture was shaken until an insoluble
layer was formed. The mixtures that no change has occurred were warmed until the formation of
turbidity.
IV.
Results and Discussions
The initial appearance of the compounds was recorded and can be seen in Table 1.
Table 1: Compounds and their initial apperance
Compound
n-butyl
Sec-butyl
Tert-butyl
Phenol
Acetone
Formaldehyde
Benzoic Acid
Acetamide
Ethyl Acetate
HCl
Appearance
Colorless
Colorless
Colorless
Red
Colorless
Clear precipitate
Colorless
Colorless
Colorless
Colorless fume
Compound
K2Cr2O7
H2SO4
Ethanol
DNPH
Tollen’s reagent
Potassium Iodide
NaClO
Fehling’s A
Fehling’s B
Anhydrous ZnCl2
Appearance
Orange
Colorless
Colorless
Dark Orange
Colorless
Colorless
Colorless
Sky blue
Colorless
Colorless goo
Each test solution undergone the different test namely, dichromate test, DNPH test,
Tollen’s reagent, iodoform test, Fehling’s test and lastly Lucas test. The changes that have
been observed on the experiment performed can be reflected on Table 2.
Tollen’s
Reagent
Iodoform
Test
Fehling’s
Test
Lucas
Test
Dark
Orange
solution,
black
precipitate
No visible
change
Yellow
solution,
red upper
layer to
clear
Indigo
solution,
light blue
precipitate
No visible
change
From
pumpkin
orange to
dark blue
green
Dark
Orange
solution,
black
precipitate
No visible
change
Light
yellow
green to
clear
Indigo
solution,
light blue
precipitate
Formed
turbidity
after
heating
3° Butyl
Precipitate
and
pumpkin
orange
layer form
Dark
Orange
solution,
black
precipitate
No visible
change
Orange to
clear light
yellow
Indigo
solution,
light blue
precipitate
Unclear
white
glass
color.
Fast
emulsion,
bubbles
at top
layer
Phenol
From layer
of red &
orange to
hot smelly
dark red
brown
From light
red to dark
orange.
Black
precipitate
Ash gray
color to
blackening
of test
tube wall.
Black
precipitate
From dirty
white
solution to
clear.
Bloody red
precipitate
From
indigo to
dark blue
Clear
solution,
red upper
layer
Acetone
From
pumpkin
orange to
brownish
solution
Yellow
orange
colloidal
precipitate
From
colorless
to very
light pink
color
solution.
Light
yellow
green to
clear.
Yellow
green
moss like
precipitate
Indigo
solution,
light blue
precipitate
Became
slight light
yellow
after
heating
Table 2
Dichromate
Test
DNPH
Test
1° Butyl
From
pumpkin
orange to
dark blue
green
2° Butyl
Formaldehyde From
pumpkin
orange to
dark cyan
blue
Yellow
ash like
precipitate
A silver
mirror
deposit
covering
the
bottom
Pumpkin
orange
color to
clear
Indigo
solution
goes up
then
subsided
to clear
color.
Dark brick
red
precipitate
formed
No visible
change
Benzoic
Acid
Dense light
yellow
condensed
precipitate.
pumpkin
orange
solution
Orange
solution.
Black
precipitate
No visible
change
Yellow
orange to
yellow
color
Light blue
upper
layer.
Indigo
solution.
No visible
change
Acetamide
No color
change
Orange
solution.
Black
precipitate
No visible
change
Light
yellow
green
solution.
White
gelatinous
web like
precipitate
Light blue
upper
layer.
Indigo
solution.
No
precipitate
No visible
change
Ethylacetate
From
pumpkin
orange to
green blue
Orange
solution.
Black
precipitate
No visible
change
Dark red
orange
color and
Black
precipitate
to dis
apperance
of the
precipitate
Light blue
upper
layer.
Indigo
solution.
No
precipitate
No visible
change
The items that are in bold letters in the table are all have positive results in the test. The
positive reactions that occur in the dichromate test are 1° butyl alcohol, 2° butyl alcohol and the
formaldehyde. First, the dichromate was added to the solutions and made the mixture have the
color of pumpkin orange, then after the addition of sulphuric acid the mixture change its color to
a dark blue green signalling that it is a positive test.
In the DNPH test, almost all of the solutions have a black precipitate besides from
acetone and formaldehyde which both have a yellow precipitate. In testing the acetone,
addition of ethanol didn’t make the mixture to have a precipitate but after adding the DNPH
mixture forms a yellow-orange colloidal precipitate. While in testing the formaldehyde,
the
the
the
the
addition of ethanol also didn’t make the mixture to have a precipitate and after adding the
DNPH, it also didn’t form any precipitate but when the mixture was heated, it formed a yellow
ash like precipitate.
In performing the Tollen’s reagent test, majority of the solutions made no visible reactions
besides from the phenol, acetone and formaldehyde. The phenol made a black precipitate while
the acetone made a very light pink color solution but what gotten our attention most is the
formaldehyde. After the addition of tollen’s reagent and warming the mixture, it made a silver
mirror effect at the bottom of the test tube.
In the iodoform test, the acetone has no visible change after the addition of potassium iodide
but when the NaClO was added, the solution became light yellow-green in color and has a moss
like precipitate. After heating the mixture, it became clear and had the yellow-green moss like
precipitate at the bottom.
The test solutions almost have the same result after undergone the Fehling’s test but the
formaldehyde is an exception. The clear color of formaldehyde became light blue after adding
fehling’s A and turned into an indigo mixture after the fehling’s B was added. The mixture was
then warmed and unexpectedly, the mixture’s volume was raised and after a second, the
mixture settled down having a clear solution and a dark brick-red precipitate.
Lastly, the Lucas test has only notable change in sec-butyl and tert-butyl. In sec-butyl the
formation of turbidity is slow and needed the mixture to be heated first before it forms the
emulsions while the tert-butyl has a significant fast emulsions. After the addition of anhydrous
zinc chloride, we waited for a while and it created turbidity.
V.
Conclusion and Recommendation
From this experiment and enough research we conclude that: In dichromate test, the
positive result is the green to blue color of the precipitate. This test is for testing if the
solution is a 1° alcohol, 2° alcohol or an aldehyde. For DNPH, the positive test is the
formation of yellow, orange or reddish-orange precipitate. DNPH is used to test the
presence of ketone or aldehyde. On the other hand, the presence of aldehydes can also be
determined by using the Tollen’s reagent test resulting into a silver mirror deposit. While the
Iodoform test is used to detect the presence of of methyl ketones and has a positive test of
formation of yellow precipitate. The formation of red precipitate is formed signalling the
presence of aldehyde using the Fehling’s test. Lucas test has the most difficult signalling of
a positive test because it has confirmatory test of appearance of emulsions or turbid
solutions. It is positive for 2° and 3° alcohols. The tests that have been used it this
experiment has a negative characterization test for phenol, acetamide, ethylacetate and
benzoic acid. To summarize things up we can refer to Table 3.
Table 3: Summary
Tests
Reagents
Positive for
Visible Results
Dichromate
K2Cr2O7
H2SO4
1° and 2° alcohols
Aldehydes
Green to blue
solutions
DNPH
2-4 DNPH
95% ethanol
Ketone
Aldehydes
Yellow precipitates
Tollen’s
Tollen’s reagent
Aldehydes
Silver mirror
Iodoform
10% KI
5% NaClO
Methyl Ketones
Yellow Precipitates
Fehling’s
Fehling’s A
Fehling’s B
Aldehydes
Red Precipitates
Lucas
HCl
ZnCl2
2° and 3° alcohols
Cloudy or turbid
solutions
It is highly recommended to be not ignorant on the effects or changes that each test
solutions has undergone and be sure to be able to record each change that have occurred.
Keep your eyes critical on judging if the a reaction has already occurred especially on the
formation of turbidity in Lucas test.Proper and organized recording of data will be a great help
for the group to minimize data errors and wrong assumption when analysing the data. Be sure
to be careful on handling these chemicals because some of them are highly corrosive. Safety
equipment are recommended to minimize accidents.
VI.
References:
 Achas M.L., Alvarez M.A., Bangot K.A., and Bayani K. 2012. Analysis of OxygenBearing Compounds. http://www.studymode.com/essays/Analysis-Of-Oxygen-BearingOrganic-Compounds-1118013.html
 http://www.lgschemistry.org.uk/PDF/Organic_functional_group_tests.pdf
 Trainor
D.,
Huang
A.,
Moyer.
2012.
Tests
for
Alcohols.
http://academics.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/Cla
ssificationTests/alcohol.html
 Trainor D., Huang A., Moyer. 2012. Tests for Aldehydes and Ketones.
http://academics.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/Cla
ssificationTests/aldehyde_ketone.html
 http://science.uvu.edu/ochem/index.php/alphabetical/s-t/tollens-test/
 2011.
Identification
of
Organic
Compounds.
http://www.123helpme.com/view.asp?id=149691
 Prof.
Robert
J.
Lancashire.
2005.
http://wwwchem.uwimona.edu.jm/lab_manuals/c10expt25.html
 McGraw-Hill
Companies.
2000.
Organic
Chemistry
4e
Carey.
http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch04summary.html
 http://chemed.chem.purdue.edu/genchem/topicreview/bp/2organic/alcohols.html#alcohol
s